Insulating bushing and electrostatic potential transformer



G. E. .JANsSoN 1,788,873

`INSULATINCT BUSHING AND ELECTROSTATIC POTENTIAL TRANSFORMER Jan. 13,1931.

`Filed Jan. 2o. 1928 lll 20 ZZ Patented Jan. 13, y1931 UNITED STATEScus'rav n. Jansson, or woLLAs'roN, nassacnrrsm'rs, nssIoNoa To connirune# Parrain' OFFICE j TBIGALMANUFACT'UBING CORPORATION, OF SOUTHBOSTON, MASSACHUSETTS, A

coaroaa'rron or 'ua'ssacnusn'rrs msunarnro RUSHING AND anamnesi-Ancro'raN'rIaL 'rnansroam Application med :tummy` ao, 192s. 4serial no.248,237.

4 This invention relates to high tensioninsulating bushings andelectrostaticV potential transformers associated therewith.A Y

` It is oftendesirable to derive small 5 amounts of power from a hightension alternating current line for the pur ose of operatin instrumentsto indicate t e voltage of the ine, for synchronizing uses and the like.

The use, of high tension electromagnetic 1e transformers for thispurpose is undeslrable because of the high cost ofthe transformers sinceAthey must be insulated against full line potential and must have aprlmary winding which will withstand full line otential. Consequently,it has been ro ose down the potential of the line y the use ofcondensers which are connected in series with the instrument and acrossthe line. The condensers allow .a small but suiciently large current to.ass, and the current, through, and the potential at, the terminal of theinsulator also been `proposed to use an insulator, as a string ofsuspension insulators as the capacif tance, the lnsulator thusperforming the double function of supplying suicient en` ergy foroperating the instrument and also for insulating the instrument from theline potential.v y l It is an object of the present invention to providea high tension insulating bushing such as used with oil filled switches,transformers,` and the like with means Vwhereby a small amount of energycan be derived from the line connected with the bushing conductor forthe operation of instruments and the like. v

A further object of the invention is the to step Figs. 2- and 3 aresectional details of modiyfied bushing constructions, wherein thecondenser plate'is protected against flash-over within the bushing.

Fig. 4 is adiagrammatic View of the elec- ,trical circuit of theinsulatorand its capacity element. ,A As here shown the oil filledbushing embodying the invention comprises upper and lower porcelainshells v'10 and 12 respectively" which are secured-in alignment 4an arecementedv to yattaching collars 14 and 16 respectively, which collarsare 'clamped together switch or transformer or, it may be, the

wall of a building.` A conductor 22 extends axially through thebushing'and has a tera high tension line and a terminal `26 at its lowerend for connection with electrical apparatus or with the movable memberof an electric switch, not shown.

A plurality of insulating tubes 28, 30 and 32 are disposed in spacedconcentric relation about said conductor 23 and the ybushino` includinvthe space between said tubes is `filled with ,011. The bushing so fardescribed is of more or less usualconstruction.

In accordance with this invention,-I provide a condenser element in theform, preferably, of a metal tube 34 which is interposed between theinsulating tube 32 and the shells 10l and 12. Said metal tube may besecured 'either to the insulating tube 32 or to the lower shell 12, or,as here shown, to both of them by bodies of cement 36 and 38respectively. An insulating ,bushing 40 is hxed iny an oil tight mannerin the attaching collar 16 and has a conductor 42 therein which extendsthrough the bushing 40 into the inte'-y rior of the shell 12 and isconnected electrically with the condenser tube 34 by ak lead 44. Saidconductor 42 is extended through the bushing and has a terminal 46 to`which a circuit leadl can be connected. The condenser tube 34 iselectrically insulated both from the high tension conductor 23 and froml. vminal 24 at its upper end for connection with follows invariationthe line potential. It has the ground and thus is caused to assume apotential the valve of which depends upon its distance from the hightension conductor, or its position between said conductor and thecollars 14 and 16, which are at ground potential, and also upon thedielectric capacity of the insulating material between said tube and thehigh tension conductor. The potential of the condenser tube can thus bemeasured by connecting a volt meter between the terminal 46 and theground and, since the potential of the condenser plate varies inproportion to variations of potential of the conductor 22, the voltmeter, if properly calibrated, wil-l read in terms of line voltage.

The amount of current which will flow through the circuit including thecondenser element 34 is a function of the area of the element; andsufficient current to operate volt meters, synchronizing instruments andthe .like can be derived from the condenser element without making saidelement unduly large and without materially decreasing the dielectricstrength of the bushing.

In the modified construction illustrated in Fig. 2, the collars 14a and16a, corresponding with the collars 1 4 and 16 of Fig. 1, are connectedby and are integral with a metal shell 48 of substantial length that hasthe attaching flange 20a located at the upper end thereof. The shell isexposed to the interior of the bushing. A condenser tube 34a is locatedwithin the bushing close to and spaced and insulated from Said shell 48,and a terminal 50 thereof is taken out of the shell through aninsulating bushing 52 located beneath the attaching flange 20a. Thefunction of the condenser tube is as described in connection withFig. 1. Annular rings 54 are connected electrically with the shell 48,which is at ground potential, and overlie and are spaced from the upperand lower ends of the condenser tube 34a and are located between saidtube and the high .tension conductor of the bushing and thus serve toprotect the condenser tube from a flashover arc, and especially one dueto a puncture of the dielectric more or less radially from the hightension conductor, the arc striking one or the other of said rings,rather than the tube.

In the modification illustrated in Fig. 3 the metal ground shell 48a,corresponding with thef shell 48 of Fig. -2, is integral with the lowercollar 16a buti's separate from the upper collar 14a, and is connecteddetachably therewith by bolts passed through flanges 56 and 58 of saidupper collar'and shell respectively. The 'condenser tube 34a is locatedwithin the bushing at and spaced from the shell 48a and the terminal 46thereof is brought out through the bushing 40, which is located abovethe supporting flange 20a of v the shell 48a. In this modification thecollars 14a and 16a have inwardly extendedl -flanges 60 and 62 which arespaced from and radially inward beyond said project into the oil spaceof the high tension bushing especially above and below the upper andlower ends of and beyond the condenser tube so that the tube, in effect,occupies a recess in the grounded shell 48 and is protected againstinternal flash over by said flanges 60 and 62.

In Fig. 4 a diagrammatic representation of the electric circuits of thecondenser elements is illustrated. In this figure, the condenser elementis connected through the primary winding 64 of a step up transformer toground and the instrument 66 is connected with the high voltagesecondary winding 68 of thel transformer. If desired, other well-knownforms of voltage or current-amplifying apparatus can be substituted forthe transformer in a manner unnecessary to illustrate. The intrumentcircuit is grounded by the conductor 7() as a precautionary measure.

I claim:

l. Aninsulating bushing comprising an outer shell, an inner high tensionconductor, an insulated condenser plate located within said shell andbetween it and said conductor and having a terminal thereof extendedthrough said shell, and a grounded metal flash-over protective memberoverlying the end of said condenser plate and projecting radially inwardbeyond said condenser plate toward said high tension conductor andproviding a shorter breakdown path between ground and said conductorthan between said conductor and said condenser plate.

2. An insulating bushing comprising an outer shell, an inner hightension conductor, an insulated condenser plate located within saidshell and between it and said conductor and having ay terminal thereofextended y through said shell, and grounded metal flash-over protectivemembers located respectively at and overlying the top and bot'- tom ofsaid condenser plate and projecting late toward said high tensionconductor an providing a shorter breakdown path between round and saidconductor than between said conductor and said condenser plate.

3. An insulating bushing having a ground tube having upper and lowervrearwardly directed Walls provided with inturned ends providing aninternal recess, insulating shells carriedby said ground tube at theends thereof, a high tension conductor extended through said vshells andtube, and an insulated condenser plate located in said internal recesswith the inturned ends'of said walls located between it and said hightension conductor and having an insulated terminal thereof extendedthrough said ground tube.

In tesimony whereof, I have signed my name to this specification.

- GUSTAV -EQJIANSSON.

